UILabel text not automatically resized using Auto Layout

I'm trying to implement a constrained UITableViewCell subclass and everything is working perfectly, except for the UILabel. The constraints that I've set up are definitely being enforced, but the text inside of the label does not resize to a smaller font size when the constraints clash. Instead, the height of the UILabel gets truncated and the font remains the same size, meaning the letters get cut off at the top and bottom.

Is there some method I have to call in order to get this to work? I would think Auto Layout would be smart enough to automatically resize the font size, so I'm kind of lost as to why this is happening.

Relevant Code:

self.label = [[UILabel alloc] initWithFrame:CGRectZero];
self.label.textColor = [UIColor whiteColor];
self.label.translatesAutoresizingMaskIntoConstraints = NO;
self.label.textAlignment = NSTextAlignmentCenter;
self.label.numberOfLines = 1;
[self.contentView addSubview:self.label];

NSLayoutConstraint *otherViewToLabelHorizontalConstraint =  // Make sure that the label is always to the right of the other view.
                    [NSLayoutConstraint constraintWithItem:self.label 
                                                 attribute:NSLayoutAttributeLeft 
                                                 relatedBy:NSLayoutRelationGreaterThanOrEqual
                                                    toItem:self.otherView 
                                                 attribute:NSLayoutAttributeRight 
                                                multiplier:1.0
                                                  constant:0.0];

NSLayoutConstraint *aTextFieldToLabelVerticalConstraint = 
                    [NSLayoutConstraint constraintWithItem:self.label 
                                                 attribute:NSLayoutAttributeTop 
                                                 relatedBy:NSLayoutRelationGreaterThanOrEqual
                                                    toItem:self.aTextField 
                                                 attribute:NSLayoutAttributeBottom 
                                                multiplier:1.0
                                                  constant:0.0];

Basically, these constraints are meant to enforce a cell where otherView is on the left, aTextField is on the right of otherView at the same y-level, and the label is below aTextField and to the right of the bottom of otherView.

As usual, thanks for any help with this.